Field of the Invention
The present invention relates to a film (hereinafter referred to as a sliding film) of a sliding portion of a shutter of an optical device such as a digital camera, formed to reduce slide friction of the sliding portion.
Description of the Related Art
In recent years, focal-plane shutters used for single-lens reflex digital cameras for example have a blade mechanism portion as illustrated in FIG. 5 as an example.
A blade mechanism portion 1 includes light shielding blades 2, blade arms 3 to drive the light shielding blades 2, and crimping pins 4 to fix the light shielding blades 2. The light shielding blades 2 reciprocate at high speed, so that opening and closing of the optical path, that is, the exposure time is controlled.
FIG. 6 is a cross-sectional view of one of the crimping pins 4 and its surroundings. The crimping pins 4 and the light shielding blades 2 are fixed to each other by crimping the crimping pins 4. The blade arms 3 and the crimping pins 4 are joined so that the blade arms 3 rotate and slide in a state having a slight gap.
In the blade mechanism portion having such a structure, since the light shielding blades reciprocate at high speed, abrasion powder may be produced in the sliding portion. The abrasion powder may fly onto optical components or sensors, possibly causing defects of an image.
Japanese Patent Application Publication No. 2008-152146 describes a surface treatment method. In this method, the whole surface of a sliding portion is coated with eutectoid plating material of fluorine-based compound, to reduce friction produced in the sliding portion including crimping pins and blade arms while reducing the abrasion powder.
In addition, Japanese Patent Application Publication No. 2010-217713 describes a method to reduce the abrasion powder. In this method, an underlying layer of nickel or nickel alloy is formed on a sliding portion, and a surface layer is formed so as to cover the underlying layer. The surface layer is made of a composite metal in which a fluorine-based compound is co-deposited.
As imaging sensors and lenses are improved, the focal-plane shutter is increasingly required to have its even faster blade speed. In addition, the focal-plane shutter is also required to stably keep its high speed performance for a long time from the beginning of use.
Thus, in the sliding portion of a shutter, some components move relative to each other at an extremely high speed, and slide on each other, while pressing each other with a small force. In the surface treatment method described in Japanese Patent Application Publication No. 2008-152146 or No. 2010-217713, the abrasion powder produced in the sliding portion can be reduced to some extent.
However, in the shutter that is coated with the eutectoid plating material, metal components will contact each other in the sliding portion in an early stage after the beginning of use, so that the frictional force may increase due to abrasion. That is, in the shutter whose sliding portion is coated with the conventional plating film in which a fluorine-based compound is co-deposited, the content of the fluorine-based compound cannot be sufficiently increased in the vicinity of the surface of the film. As a result, the blade speed may change significantly in a relatively early stage after the beginning of use. As countermeasures to this, a pre-conditioning interim operation could be performed until the blade speed becomes stable, before the shutter is shipped as a product. However, this may increase cost.
For this reason, there is desired a sliding film which keeps its low friction from when the sliding film was produced, and which hardly changes its frictional force even when a user continues to use the sliding film.